A wide range of medical treatments have been previously developed using “endoluminal prostheses,” which terms are herein intended to mean medical devices which are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring or artificially made lumens. Examples of lumens in which endoluminal prostheses may be implanted include, without limitation: arteries, such as those located within the coronary, mesentery, peripheral, or cerebral vasculature; veins; gastrointestinal tract; biliary tract; urethra; trachea; hepatic shunts; and fallopian tubes. Various types of endoluminal prostheses have also been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted lumen wall.
For example, stent prostheses have been previously disclosed for implantation within body lumens. Various stent designs have been previously disclosed for providing artificial radial support to the wall tissue, which forms the various lumens within the body, and often more specifically within the blood vessels of the body.
Cardiovascular disease, including atherosclerosis, is the leading cause of death in the U.S. The medical community has developed a number of methods and devices for treating coronary heart disease, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
One method for treating atherosclerosis and other forms of coronary narrowing is percutaneous transluminal coronary angioplasty, commonly referred to as “angioplasty,” “PTA” or “PTCA”. The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. The procedure is accomplished by inflating a balloon of a balloon catheter within the narrowed lumen of the coronary artery. In some instances the vessel restenoses chronically, or closes down acutely, negating the positive effects of the angioplasty procedure.
To provide radial support to the treated vessel in order to prolong the positive effects of PTCA, a stent may be implanted in conjunction with the procedure. Effectively, the stent overcomes the natural tendency of the vessel walls of some patients to close back down, thereby maintaining a more normal flow of blood through that vessel than would be possible if the stent were not in place. Under this procedure, the stent may be collapsed to an insertion diameter and inserted into a body lumen at a site remote from the diseased vessel. The stent may then be delivered to the desired site of treatment within the affected lumen and deployed to its desired diameter for treatment.
Access to a treatment site is most often reached from the femoral artery. A flexible guiding catheter is inserted through a sheath into the femoral artery. The guiding catheter is advanced through the femoral artery into the iliac artery and into the ascending aorta. Further advancement of the flexible catheter involves the negotiation of an approximately 180 degree turn through the aortic arch to allow the guiding catheter to descend into the aortic cusp where entry may be gained to either the left or the right coronary artery, as desired. Because the procedure requires insertion of the stent at a site remote from the site of treatment, the device must be guided through the potentially tortuous conduit of the body lumen to the treatment site. Therefore, the stent must be capable of being reduced to a small insertion diameter and must be very flexible.
One particularly flexible stent is available from the assignee of the present invention, Medtronic Vascular, Inc., and is known as the S7 STENT (shown generally as stent 101 in FIG. 1A). The S7 STENT has several rows of cylindrical segments, in this case sinusoidally shaped segments 102, which are welded together at the apexes 104 of adjacent segments. FIG. 1A shows stent 101 crimped onto an expandable balloon 106. Alternatively, the stent may be made of superelastic material such that it is positioned in a compressed state and naturally expanded within a body lumen. The shape of the sinusoidal segments is described in U.S. Pat. No. 6,344,053 to Boneau, the disclosure of which is incorporated herein by reference in its entirety.
However, stents come in a variety of shapes and sizes. For example, stents formed from a helical winding of wire are useful for covering the walls of a stent while being particularly flexible. An example of a helical winding can be found in U.S. Pat. No. 4,886,062 to Wiktor, the disclosure of which is incorporated herein by reference in its entirety. FIG. 1B shows a stent 107 having a wire formed into a series of helical windings 108, in this case sinusoidally shaped helical windings 108. The windings 108 form rows along the length of the stent 107. Just as in FIG. 1A, FIG. 1B shows stent 107 on an expandable balloon 110. However, stent 107 could be a self-expanding stent, such that once positioned within a body lumen, it naturally expands.
In another example, U.S. Pat. No. 6,565,599 to Hong et al., the disclosure of which is incorporated herein by reference in its entirety, describes rows formed from sinusoidally shaped segments which are interconnected by elongated struts of a flexible polymer material, which hold the rows apart from one another. U.S. Pat. No. 6,475,237 to Drasler et al., the disclosure of which is incorporated herein by reference in its entirety, describes a strut wherein a portion thereof is made thinner and more flexible such that the strut can flex at those locations. However, the struts in these applications are formed as one piece. Thus, one portion of the strut cannot move independently of a separate portion of the strut. Further, these struts do not allow the strut rotational movement because each end of the strut is permanently coupled to adjacent rows.
Further, U.S. Pat. No. 5,035,706 to Gianturco, the disclosure of which is incorporated herein by reference in its entirety, describes the use of interlocking rings to connected adjacent segments. However, these interlocking rings, while providing improved flexibility over a strut, do not allow the segments to lay flat against the walls of the sides of the lumen. U.S. Pat. No. 6,387,122 to Cragg, the disclosure of which is incorporated herein by reference in its entirety, describes a helical stent in which subsequent windings are connected by loop members made from sutures, staple or rings of metal or plastic. Connecting rows of a helical stent, provides more contact between the stent and the lumen walls (i.e., more scaffolding) and thus provides better support for the lumen wall.
Thus, one object of stent design is to improve flexibility between adjacent rows, such as those formed by either cylindrical segments or helical windings, in order that the stent may move more easily through the tortuous body vessels to a treatment site.